CONDITIONS AT THE TIME OF ASH DEPOSIT 609 



of green bentonite with streaks of white calcium carbonate extending 

 through it in nearly vertical lines; then 5 inches of yellowish, sandy ben- 

 tonite containing rounded grains of quartz, biotite mica, and feldspar, 

 and a basal layer of 5 inches of green bentonite resting on a smooth sur- 

 face of dark blue, crystalline limestone. This middle coarse layer might 

 have been caused by a shifting of prevailing winds or an increase in their 

 intensity. The contacts between the three layers of the bentonite bed arc 

 very regular, but that between the top of the bentonite and the overlying 

 limestone is irregular and, in places, this dove-colored, thinly bedded 

 limestone lies within one or two inches of the top of the second layer of 

 the bentonite bed. This regular bedding with a middle coarse layer of 

 impure bentonite indicates water deposition, practically continuous, but 

 the irregular contact of the bentonite with the overlying limestone shows 

 that the bentonite, after deposition, was subject to erosion, probably by 

 current or tidal action, or by wave action due to a nearer progressing of 

 the shoreline of the Lowville Sea to this point during Le Ray time, when" 

 the Lowville Sea probably became greatly constricted, due to the slight 

 warping of the earth's crust. 



Thickness of Bentonite Layer 



When a volcanic ash deposit covers a shallow inland sea like the Low- 

 ville was during Le Ray time, the bulk of the ash would finally settle 

 on the sea bottom directly below that part of the sea surface on which it 

 fell. In places local currents might carry and redeposit a small amount 

 of the ash in irregular fashion, but, taken all in all, the greater the dis- 

 tance from the ancient volcano producing this ash, the less would be the 

 thickness of the ash deposited on the sea-floor. This being the case, the 

 present bentonite deposit would get thinner and thinner as one progressed 

 away from the old volcanic center. 



The maximum thickness of the bentonite bed measured was at High 

 Bridge, Kentucky, where it is considered to average 5 feet, although as 

 much as 10 feet is stated to occur at one point. To the south of this 

 place, on the Kentucky-Tennessee line, in wells drilled for oil in Pickett 

 County, Tennessee, 4 feet of this bentonite was encountered, while about 

 5 miles still farther southward, at Pikeville, Tennessee, only 3 feet of 

 bentonite occurs. Southwest of Pikeville, at Singleton, Tennessee, at a 

 still greater distance from High Bridge, Kentucky, the bentonite meas- 

 ured 2 feet thick, and at Birmingham, Alabama, the southernmost place 

 measured, it is only 14 to 19 inches thick. These figures show a gradual 

 thinning of this ash bed as one goes south from High Bridge, Kentucky, 



